Contact Nostalgic Air.
Nostalgic AC - Complete A/C Kit Mopar Vehicles - Select an Evaporator
They have kits to fit the slant 6, includes the pulley.
You should not have any clearance issues between your fan/radiator, as nothing changes (dimensionally) with A/C. As previously stated, the condensor mounts in FRONT of the radiator, not between the radiator and engine.
NACP requires you to select an evaporator for your kit, I think you would be well-advised to contact them directly (1-888-977-8889) to assist with your parts selection.
Also be aware that you will most likely need to install a radiator shroud along with your A/C installation.
